The invention relates to methods of preparing rod-like nanometer scale carbide materials.
Examples of rod-like nanometer scale carbide materials (hereafter termed "nanorods") having diameters less than 100 nm and aspect ratios from 10 to 1000 have been reported. The carbide nanorods are physically distinct from rod-like carbide materials termed "whiskers" that have solid crystalline structures with diameters generally between 1 and 100 microns, although diameters as small as 0.1 micron have been observed. The small diameters of carbide nanorods lead to enhanced properties relative to larger-sized whisker materials.
Methods for preparing SiC and other carbide nanorods involve reaction between a volatile main-group (e.g., Si, B) or metal (e.g., Ti, Fe, W) species and a carbon nanotube which serves as a template for the growth of corresponding carbide nanorods (e.g., SiC, TiC). This method can also be used to prepare carbide whisker materials having diameters between 200 and 400 nm. The method provides carbide nanorods on a small scale (i.e., laboratory scale), but is difficult to scale up due to the expense and limited availability of the carbon nanotubes.
The most widely used commercial method used for producing SiC whiskers involves carbothermal reduction of silica (SiO.sub.2) with rice hulls. There are other methods reported for the growth SiC whiskers that involve "seeding" elements, such as the rare earths, Group IA, Group IB, Group VB, Group VIB, Group VIIB, and Group VIII of the Periodic Table of Elements, to facilitate production of whiskers. See, for example, Qi, et al., U.S. Pat. No. 5,221,526. Similar metal catalysts have been used in the preparation of carbon fibrils. See, for example, Snyder, et al., WO 89/07163.